The specific objectives are 1) to further our understanding of the molecular mechanisms involved in the phenomena of patching and capping induced by ligand-surface receptor interactions; 2) to obtain information on the regulatory processes involved in the biosynthesis and mobility of membrane proteins and viral-coded glycoproteins. In order to determine the biochemical composition of the lymphocyte cap structure, we have employed both immunolactoperoxidase labeling and density perturbation isolation techniques. Isolated lymphocyte cap structures have been found to contain almost a full complement of surface membrane proteins. Analysis by SDS-PAGE plus autoradiography reveals that at least two surface polypeptides are enhanced and one is significantly decreased in the "cap" fraction compared to the whole cell homogenate. This finding is taken as further evidence for the selective redistribution of certain membrane proteins during lymphocyte capping. During the course of studying biosynthesis of membrane proteins, we have used immunoferritin staining techniques at the electron microscope level to localize the viral glycoprotein, gp69/71, in murine T-lymphoma cells. We have found that gp69/71 molecules are located within the following areas of the cell: 1) aggregations of small clusters at the terminal regions of flattened endoplasmic reticulum (ER) cisternae; 2) small clusters enclosed within membraneous vesicles near the ER; 3) accumulations of clusters close to or beneath the plasma membrane within unidentified compartments; 4) individual molecules arranged in a random pattern on the surface of the plasma membrane. These findings support a large number of previous biochemical reports concerning the biosynthetic pathway and transport of membrane glycoproteins.